Preparation and mechanism analysis of non-contact respiratory sensor based on ZnO/RGO composites

A humidity sensor based on zinc oxide (ZnO) and reduced graphene oxide (RGO) composites (ZnO/RGO) for non -contact respiratory detection was fabricated by hydrothermal method, and the sensing mechanism of ZnO/RGO was studied by the first principle based on density functional theory. Experiments show that RGO effectively improves responsivity, linearity and hysteresis of ZnO humidity sensor. Compared with ZnO, the resistance of ZnO/RGO humidity sensor achieves 4.5 orders of magnitude with high response of 48282, maximum hysteresis rate of 3.1%, response/recovery time of 2 s/11 s and the best linearity in a range of 11% -95% RH. First principle calculation shows that the addition of RGO can reduce chemical adsorption energy and enhance physical adsorption energy of ZnO to water molecules, which explains mechanism for the enhanced performance of ZnO/RGO humidity sensor. Furthermore, ZnO/RGO humidity sensor has been successfully used for non -contact detection of respiration frequency under different breathing states, where a simple circuit is designed to realize the visual detection of humidity signal, which shows that ZnO/RGO materials has a practical value in personal medical services and smart health electronic devices.